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108. Airborne Gamma-ray Spectrometry (1970)

Starting in the 1930s, Canadian geologists and prospectors used Geiger counters to find deposits of uranium. These were replaced in the mid-1960s when airborne radioactivity surveys became practical following the development of large, sodium iodide scintillation detectors and compact electronic instrumentation. Scientists at the Geological Survey of Canada realized that these detectors and advanced electronic technology could not only detect the radiation emitted by naturally occurring uranium, thorium, and potassium, but could also measure natural gamma-ray spectra in real time.

In the late 1960s, Quentin Bristow developed and tested a gamma-ray spectrometer system. By 1970, the airborne gamma-ray spectrometer was ready for routine surveys. The system, installed in the Survey’s Skyvan aircraft, was used to assist in geological mapping, mineral exploration, and environmental monitoring.

Continuing improvement of sodium iodide detectors and digital electronics led Bristow and his Survey team to design and construct an improved, full spectrum recording airborne gamma-ray spectrometer. It was first used in 1978 to support Operation Morning Light, which searched for debris of a nuclear-powered Soviet satellite in the Northwest Territories. For the following 20 years, it mapped geological distributions of radioactivity, setting world standards for airborne gamma ray spectrometry surveying.